Preparation of cyclopentadiene



Patented Mar. 23,, 1948 Robert MjK'e'nnedy,

Hetzel, Cheltenham, Pa.

Company, Philadelphia,

New Jersey Drexel Hill, and" Stanford J. assignors .to Sun Oil Pa., a corporation "of No Drawing. Application August 19, 1947, Serial No. 769,523

5 Claims. 1

This inventionrelates tocyclization, Specifically it relates to the dehydrogenation and cyclization of dehydrogenatable hydrocarbons, having 5 carbon atoms-per-molecule, especially 1,3'pentadiene. More specifically the invention is concerned with a commercially feasible process for the conversion of pentane or 1,3 pentadiene to 1,3 cyclopentadiene by converting the saturated material to 1,3 pentadiene and cyclizing the 1,3 pentadiene to 1,3 cyclopentadiene.

As stated, the invention isapplicableto the dehydrogenation and cyclization of'pentane to 1,3 cyclopentadiene. This conversion is considered to take place by way of l-pe'ntene and 1,3 pentadiene. Accordingly, the invention will be described with reference .to the conversion of 1,3 pentadiene to 1,3 cyclopentadiene to which it is pre-eminently suited. These reactions can be represented as follows:

( a 1 3 cyclopentadlene 0 112 According to the invention 1,3 pentadiene in pure form, or admixed with normal pentane and/or normal pentenes, or other gases, is contacted with subdivided iron or steel at an elevated temperature for a time suificient to efiect a desired extent of conversion to 1,3 cyclopentadiene. The subdivided contact mass according to the invention can be composed of jack chain or other suitably divided iron or steel.

The temperature employed for the dehydrogenation of the hydrocarbon, in the instant case 1,3 pentadiene, will vary depending upon the other conditions of operationtandton the nature or purity of the charging stock. Hdweverfthe conversion .of. l,3.'pentadien'e 'canbe advantageously effected at: a temperature "within :the range 300 C. to a temperature above whichiisubstantial decomposition of the?hydrocarbons will take place. Morespecifically a temperature-within the range 400 C.-'700 0., preferably 450 C.- 650 C., can be employed.

While the conversion per pass is substantially independent or pressure "it has 'been found that lower pressures'seem'to form higher :yields on recycling. Accordingly, while higher :and lower pressures are not 'excludedirom'the scope of the invention, pressures in the range .of :1000 I mm. Hg-10inm II-Ig, vpreferably120i) mm. rig-'10 mm. Hg, can be employed.

The time of contact of the 1,3 pentadiene with the subdivided iron or steel is a factor to beconsidered. There is an optimum range of contact time corresponding to charging rates of 0.25 gram/minute/lOO grams-10 grams/minute/ grams of subdivided iron or steel. However, higher and lower charging rates are not excluded from the scope of the invention.

Example 1 1,3 pentadiene of about 88% pentadiene content was fed to a reaction tube consisting of a length of ordinary carbon steel pipe approximately one inch inside diameter. having a volume of 128 cc. and packed with 100 grams of jack chain, manufactured by the Hodell Chain 00., Cleveland, Ohio, and designated No. 18, Bright. The pipe was maintained at 650 C. by external means and the system was evacuated in a controlled manner such that while the liquid pentadiene was being fed into it the pressure remained at 15 mm. Hg absolute pressure. Means were provided for vaporizing the 1,3 pentadiene before it entered the reaction tube and preheating it to approximately 600 C. The rate of feed was maintained at a constant value of about 0.5 gram/minute/lOO grams of contact mass. The products were condensed and analysis for cyclopentadiene showed a once-through yield of 9.2%. Other products (gas, polymer, etc.) were obtained to the extent of 10% so that by recyclizing the unreacted 1,3 pentadiene an ultimate yield of approximately 48% cyclopentadiene would be obtained.

Example 2 With the same apparatus and technique as in Example 1 the same charge of 1,3 pentadiene was vided iron or steel as set appended claims.

3 cyclized at 750 C., 15 mm. Hg and a charging rate of 0.5 gram/minute/IOO grams of contact mass. A once-through yield of cyclopentadiene of 6.0% was obtained. Other products (gas, polymer, etc.) were obtained to the extent of 13.5% resulting in a calculated ultimate yield of 31% cyclopentadiene.

The contact mass can be regenerated indeIinitely to substantially its original activity.

When using a contact mass of discrete particles the particle or pellet size can be varied. About 4 to 8 mesh has been found quite satisfactory. Obviously the particle size should not be too small in the sense that a large pressure drop across the contact mass is to be avoided if substantially the same pressure in all parts of the apparatus is desired, unless fluid or fluidized operation is em ployed.

It will be apparent to those versed in the art that modification and variation are possible within the scope of the invention as defined in the appended claims, the essence of the invention being in that dehydrogenatable hydrocarbons having by hydrocarbons present will take place for a time sufiicient to elTect a desired extent of conversion.

2. A process for the dehydrogenation and cyclization of 1,3 pentadiene to 1,3 cyclopentadiene which comprises contacting 1,3 pentadiene with a contact mass selected from the group consisting of subdivided iron and steel at a temperature ,'Within the range 400 C.-700 C, for a time sufiicient to effect a desired extent of conversion.

3. A process according to claim 2 wherein the pressure is in the range of 1000 mm. Hg.-10 mm.

4. A process for the dehydrogenation and cyclization of 1,3 pentadiene to 1,3 cyclopentadiene which comprises contacting 1,3 pentadiene with a contact mass selected from the group consisting of subdivided iron and steel at a temperature within the range 450 C.-650 C, at a pressure within the range 200 mm. Hg-10 mm. Hg for a time sufficient to effecta desired extent of conversion.

5. A process according to claim '4 wherein the charging rate of 1,3 pentadiene to the contact mass is within the range 0.25-10 grams/minute/ grams of subdivided iron or steel.

ROBERT M. KENNEDY. STANFORD J. HETZEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

